If a poster consistently informs us that, say, Russian field guns were ineffective because their wheels were made of green cheese, the rest of us will learn soon enough to disregard his or her posts.

In case this poster is asked from where he or she derived this information - he should be able to give a source, even in a light hearted discussion.
Then one is able to cross check, as positive example see my discussion with Bill where he gives me a quote from Petre which I could check and go on with the discussion in a hopefully constructive manner.
Otherwise such "discussions" made end in just tit for tats, ending in a continous circle and not making any progress, which happen frequently here also.